What best describes integral drift in an INS and how is it mitigated in a fused navigation system?

• A. Integral drift arises from biases accumulating over time in the inertial sensors.
• B. Integral drift arises from biases accumulating over time in the inertial sensors; mitigated by GNSS/odometer updates, zero-velocity updates, and sensor calibration.
• C. It is due to random measurement errors in GNSS; corrected by Doppler.
• D. It's the drift of the computation due to CPU rate; solved by increasing sampling frequency.

Answer: (B)

Integral drift comes from biases in the inertial sensors that, when their outputs are integrated over time, cause the estimated position and velocity to steadily diverge. Those biases are systematic, so the error grows quadratically with time as integration accumulates. In a fused navigation system, this drift is countered by tying the INS to external references. GNSS and odometer updates provide independent position and velocity information that corrects the INS trajectory. Zero-velocity updates help when the vehicle is known to be stationary to reset or constrain the bias estimates, and sensor calibration reduces the biases themselves, lowering the drift rate. Doppler corrections relate to GNSS velocity measurements, not directly to removing INS biases, and simply increasing the sampling rate doesn’t remove the bias-driven drift.